Extra desktops no longer functional

I can no longer drag open windows from Mission Control into additional desktops. I used to have 2 desktops open; one for work things, one for personal things; now everything is open under Desktop 1 and if I try drag anything into Desktop 2 it shows a small grey no entry sign, as if it isn't active. However, if I click on Desktop 2 everything just transfers to that desktop and then Desktop 1 becomes inactive.

I know it's a setting that is just switched off somewhere since I updated and I have followed advice from multiple threads, but nothing has fixed it.